Tinnitus is a medical term for acoustical perceptions heard in the ear(s) or head, not produced by external sound. This sound can be experienced as a ringing, buzzing, whooshing, or hissing. Estimates suggest that as many as 50 million people in the United States experience tinnitus to some degree. Approximately 12 million of these people experience tinnitus bothersome enough to seek medical treatment. Two to 3 million Americans are severely affected by their tinnitus to the extent that their ability to function is severely impaired.